We took a rare tour of one of the US Navy's most dangerous warships — nicknamed the 'Sledgehammer of Freedom'

The USS John Warner, a Virginia-class attack submarine commissioned in 2015, is the US's third-newest sub.

We got the chance to tour the Warner as it was docked at Naval Station Norfolk.

Named after the former US senator John Warner — but nicknamed the "Sledgehammer of Freedom" by the crew — the Warner can perform a variety of missions for the US Navy, including surveillance, reconnaissance, and search and rescue, as well as launch land-attack missiles, torpedoes, and mines.

The Warner, and submarines in general, is highly classified and rarely seen by the public.

We entered the upper level of the ship, and this was our first glimpse inside. As you can see, it's a little tight in there.

"This is actually how we would get SEALs off the ship submerged," Eichenlaub said. "So you would stick a platoon of SEALs in here, 14 guys ... you fill this chamber with water until you match the outer sea pressure. Once the pressure in and outside the ship match, the hatch will lift off open, and they can swim out of a fully filled chamber into open ocean."

Once there, the SEALs can retrieve any weapons or gear from the SOF box (which we saw being loaded into the tower in the first picture).

A short video gives an even better look at the hatch that leads to open water.

As we made our way to the middle level, we ran into a group of sailors performing a preventative maintenance check of the ship's electrical components.

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On the middle level, we saw the flare and countermeasure launcher, situated in a small office.

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Across the hall from the countermeasure launcher is a food closet, one of many that the ship needs to feed the crew for months at a time.

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The closets go back about 15 feet, Eichenlaub said, and are packed strategically so the crew can essentially eat there backward.

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Service members eat here in the chow hall, the largest open space in the ship. There's even a soft-serve ice cream machine on the right.

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On the opposite wall hangs the literal "Sledgehammer of Freedom." The crew began calling the Warner that after the commander used the moniker in a speech before their first deployment.

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This one is for the crew, while officers have their own: "the Sledgehammer of Democracy."

The officers, on the other hand, eat in the officer's chow hall and are served by kitchen staff through the door in the back right. The commander sits in the star chair in front of the "Sledgehammer of Democracy."

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Here's a close-up.

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This is mission control, the most classified area of the ship. As such, all the monitors were turned off, and we cropped, blurred, and darkened anything sensitive.

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Sonar, fire control, and navigation computers are all in mission control. Eichenlaub goes into detail about mission control in this short video.

The sonar system onboard is designed with a Large Aperture Bow Array that uses life of the hull hydrophones to detect sound waves produced by other ships and even sea life.

The sonar computers.Daniel Brown/Business Insider

The Warner, interestingly, does not have a periscope and instead uses photonic masts built into the outside tower that provides a view above water that feeds into any monitor on the ship.

Eichenlaub then told us more about fire control, where torpedoes and cruise missiles are launched.

And this computer is where flares and countermeasures are launched.

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This nine-second video shows the two voyage-management systems, which plan and navigate the ship.

As we exited mission control, Eichenlaub showed us what the crew calls the Fishbowl.

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Sailors assigned to the ship are not considered submariners until they receive their warfare qualifications saying they are proficient in every system aboard. Until then, their personal seals are put in this case for motivation.

Every US submarine has a "fishbowl."

The bunks for sailors, or berthing areas, are spread out all over the ship.

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And they're a little snug.

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Eichenlaub showed us the XO's sleeping quarters.

Now let's enter the torpedo room. Behold!

Using a "pump-jet propulsor," Mark 48 Advanced Capability torpedoes can travel at more than 50 mph — but its top speed is technically classified.